The Adhara<->Agena run isn't bad. Very short run, trading Indu for Medi, Low to High for each. This may possibly be the most profitable 2-stop run there is, actually, provided your convoy doesn't get torn apart by pirates. I haven't worked out any 3- (or more) stop runs in any definitive manner, but for 2-stops, there are few better. A round trip earns you 378 per ton gross (before paying for your escorts - figure 19/ton/day for light freighters).
Theoretically, the most profitable 2-stop run would involve trading medi for luxu, both low to high, but I don't know of any planet combos that will allow that. The second highest theoretical would be trading low->high between medi and equi, but again I don't know if that's actually possible. The Agena->Adhara run is the third highest theoretically, and the highest in reality.
Actually, the same indu<->medi run is also possible between a few other planets, but Agena<->Adhara is also the SHORTEST indu<->medi run out there.
Since this run is two jumps long, the net take on a round trip (4 jumps plus 2 days planetside) = 378 - 6*19 = 264 credits/ton using light freighters. At 150 tons per l.freighter, that equals 39,600 net profit per round trip per freighter.